It is well known, such as in U.S. Pat. No. 4,118,597 to D. F. Proctor et al. of Oct. 3, 1978, to take advantage of the hysteresis characteristic of a magnetic structure to measure electrical line current by using that line current to magnetically adjust the structure by means of line current windings electromagnetically linking the structure so that a sensing circuit also electromagnetically linking the structure by sensing windings can detect the magnetic adjustment and can provide an electrical output which is a measure of the amplitude and polarity of the line current. Such arrangements have taken advantage of changes in permeability of the structure due to changes in line current to effect the detection. Such detection of the changes in permeability has taken the form of detecting changes in the alternating-current impedance of the sensing circuit caused by the changes in permeability.
Such arrangements as in the above prior art must contend with the fact that the sensing circuit will provide an electrical output at all times and that such output must be calibrated for all conditions of the line current, including zero line current.